A couple on holiday in Fiji stumbled into a murder case gripping the Pacific island nation when their stroll on an idyllic beach led to the discovery of a human head.

It was the latest in a series of gruesome finds that began two weeks ago, when dismembered feet – wrapped and weighed down with rocks - washed up at Natadola beach, a popular tourist destination in the former British colony.

Police have since found numerous other body parts – typically wrapped in cloth or netting and weighed down – which had all washed onto the beach.

The latest find was made by Graeme Bickley, a New Zealand businessman who was enjoying a morning beachside stroll with his wife Jan when he spotted a submerged green bundle tied with nylon rope.

"We said, just jokingly, that it was more body parts," he told AFP.

"Then when I waded in to grab it, it became apparent how heavy it was, it almost pulled me over.”

Mr Bickley said he “wasn’t game” to look inside the bundle but turned it over to police, who later confirmed its grim contents.

“Someone has very callously cut them up, then spent a lot of time weighting them down with rocks and neatly knotting them up,” Mr Bickley said.

"They obviously didn't expect it to come back to shore."

The head appears to be linked to the murder of Yuri and Natalia Shipulin, an expatriate Russian couple who went missing on June 16.

The couple moved to Fiji in 2011 and ran a photography business from their vegetable farm in the Fijian highlands. Police believe a chainsaw was missing from the farm.

Authorities in Fiji have conducted DNA tests on the body parts and confirmed they belonged to the Russian couple.

“"We're still waiting for the Interpol [test] but we have tested it on our own," Assistant Commissioner Luke Navela told ABC News.

“Our investigators are walking the same area to get as much information as possible to lead us to [solve] this case."

No motive has yet emerged for the murders.

Their land rover was found near the beach, apparently with the keys in the ignition and the couple’s phones and other belongings untouched.

Some reports have suggested the couple were staying at a resort about 30 miles from the beach and were last seen having a drink there.

The couple’s disappearance was initially reported to police by Andrew Luzanenko, a business partner who said the farm had been struggling since Cyclone Winston earlier this year.

"Yuri was very depressed," he told The Fiji Times shortly after the couple disappeared.

"His business is not doing very well especially after the cyclone and then we tried to revive the farm but it has been a very slow process."

Alla Mallerich, a friend of the couple, described the pair as "soul mates".

"Yuri was a happy, easy going man who loved life, loved Fiji and he had plans to build his life in Fiji," she said.

Interestingly, Russia has been expanding diplomatic ties with Fiji in recent years as it tries to expand it influence in the Pacific.

Earlier this year, Russia made a secretive donation of 20-containers of arms to the Fijian military – a move that raised concerns that Moscow was seeking to build an armed presence in the area.Fijian authorities said the arms were for use by the country’s peacekeeping forces, who frequently serve in United Nations missions.

No connection between Russia’s growing Fijian ties and the unusual murder has emerged.